A conventional MSe analytical technique comprises performing chromatographic separation on a sample to be analysed, ionising the sample to generate precursor ions and then directing the precursor ions into a fragmentation device that is alternated between a low fragmentation mode and a high fragmentation mode. Precursor ions are substantially not fragmented in the low fragmentation mode and are subsequently pass to a mass analyser for mass analysis, whereas precursor ions are fragmented in the high fragmentation mode and the resulting fragment ions are subsequently passed to the mass analyser for mass analysis. The chromatographic retention times that are related to the periods in which the precursor and fragment ions are detected are known and can be used to correlate a precursor ion to a fragment ion. This technique has proven to be particularly useful in analysis that requires unbiased fragmentation approaches and quantitative information. However, this technique provides only limited confidence that the precursor ions are correctly associated with their related fragment ions.
MSe techniques have been improved by separating the precursor ions according to their ion mobility prior to their fragmentation and maintaining the temporal fidelity of the ion mobility separated precursor ions and of the fragment ions. The elution profile and elution times from the ion mobility separator are then used in conjunction with the chromatographic information so as to improve the confidence of associating precursor ions with their related fragment ions. This technique is commonly known as HDMSe. However, this improved technique still only provides limited confidence that the precursor ions are correctly associated with their related fragment ions.
It is therefore desired to provide an improved method of mass spectrometry and an improved mass spectrometer.